Method of chemically curling animal hair with sulfur dioxide in aqueous solution



Patented Sept. 17, 1357 ll/IETHOD OF CHEP/HCALLY CURLHNG ANIMAL HAIR WITH SULFUR DEGXHDE 1N AQUEUUS SQLUTIGN Application October 24, 1951, Serial No. 253,698

8 Claims. (Cl. 8-1275) No Drawing.

This invention relates to a method of chemically curl ing hair or the like. More particularly, this invention relates to a method of spontaneously curling hair, such as hog hair, cattle hair and horse hair, for use in upholstering furniture. This invention also has utility when applied to other keratin-containing filamentary tissue, such as wool, feathers, fur, etc.

It has long been the practice to use animal hair for upholstery and cushioning purposes and for other uses in which resiliency is a factor. It has been customary to employ for this purpose cattle tail hair, horse tail hair, horse mane hair, and hog hair. These hairs are normally rather straight. To provide the desired cushioning properties it is customary to curl the hair.

The usual method of imparting a curl to animal hair has been to form a rope from the hair and setting or fixing the curvature so imparted to the hair by subjecting the rope to the action of water at or near the boiling point. Alternatively, an atmosphere containing steam can be used. The rope is then dried and finally opened to thereby release the individual strands of curled hair.

The rope may be either hand or machine spun. In either case it is customary to blend different types of hair to meet requirements of both loft and resiliency, and cost limitations. Also, it is usually necessary to blend some long hair with short hair before the latter can be successfully roped and curled. Tail and mane hair are long and relatively expensive whereas hog hair is short and inexpensive. In order to curl hog hair, then, it is sometimes customary to add say from to 25% of expensive long hair.

The long hairs, e. g. cattle tail, horse tail, and horse mane, run around six to eighteen inches in length. Hog hair, collected during the winter season, measures about 1 /2" to 3%" in length, averaging perhaps 2 /2". Shimmer hog hair will run from /2" to about 3", with the average being about 1 /2". The latter is usually considered too short to be curled for upholstery purposes although it may be that some is used in adrnixture with winter hog hair.

The cost of curling hair in the manner described is substantial and adds considerably to the cost of the original hair. There is an obvious need for a less expensive way of curling hair and for a means for curling short hair which does not require blending with long hair.

It is therefore an object of this invention to provide a less expensive method for curling hair for use in upholstering furniture, and to provide a method which will avoid the necessity of combining long hair with short hair to carry out the curling process. More specifically, it is an object of this invention to provide a method for curling hair or the like involving the use of a chemical treatment and resulting in the spontaneous curling of the hair. Still more specifically, it is an object of this invention to develop a method for spontaneously curling hair by means of which a controlled statistical curvature can be imparted to the hair without any serious impairment of the desirable physical properties of the hair for use in upholstering, such as tensile strength, resiliency, and elongation at break. Further objects and advantages of this invention will appear as the specification proceeds.

Hair can be defined as a filamentary epithelial tissue composed mainly of keratin. Keratin in turn is a fibrous protein molecule containing at intervals within the polypeptide chain of amino acids the unique amino acid cystine.

The physical and chemical structure of hair has been under intensive investigation in recent years but there is still a great deal concerning the structure of hair that is not completely understood. Hair is composed essentially of keratin molecules which are long protein fibrous molecules oriented for the most part lengthwise of the hair filament. These keratin molecules comprise long polypeptide chains which include the amino acid radical cystine. This cystine radical provides disulfide bonds which crosslink parallel polypeptide chains. In addition to the disulfide cross has between adjacent polypeptide chains there are presumably other Weaker forces, such as hydrogen bonds and salt linkages. X-ray difiraction data has led most specialists in the field to believe that the keratin molecule normally exists in a series of undulating folds and this is generally referred to as a form of keratin. It is presumed that many of the excellent elastic properties of hair are the result of this unusual configuration. When hair is subjected to strain while wet, it will become stretched and it is presumed that the folds in the keratin molecule are in some measure unfolded. This unfolded state is known as [5 keratin. The internal stress caused by the deformation of the keratin folds will restore the hair to its original length when the tension is released. However, if the temperature is suficiently high the hair will assume a permanent elongated shape and this is considered to be due to a momentary rupture of some of the crosslinking forces and the reconstituting of these forces in positions which no longer subject the keratin molecule to internal stresses that would tend to restore the hair to its original length.

Originally the forces within the hair filament are in balance when the hair is substantially straight. When hair is curled by the mechanical process as in the prior art, external forces in roping the hair compel the hair filaments to assume a curvature in opposition to the normal forces acting on the hair. Treatment with boiling water momentarily ruptures certain over-stressed bonding forces within the keratin molecules which are immediately reconstituted in such a manner as to result in a new balance of forces compatible to the retention of the new form of the hair. This is accomplished without significant alteration in the overall length of the hair.

It has been known for sometime that the disulfide crosslinkages could be ruptured with reducing agents, and thereafter that the cross-linkage bonds could be reformed with oxidizing agents or other cross-linking agents. This information has been applied in the cosmetic industry to the curling of human hair by chemical treatments involving the steps of: 1) reducing some of the cystine cross-linkages, (2) positioning the hair in the desired curled form manually, and (3) setting the curl by chemically reconstructing the crystine cross-linkages. This process is popularly known as the cold-wave process for curling hair and is generally carried out at around room temperature 25 C.) or slightly above. Such cold-wave processes of curling hair do not result in the spontaneous curling of the hair, but instead require the manipulative forming of the desired curl, and thus are distinct from the process of this invention. It will be apparent that a method of curling hair requiring the mechanical manipulation of the hair to efiect a desired form would have relatively little advantage when applied to the curling of hair for upholstering purposes over the previously employed mechanical method.

This invention involves the discovery that hair or the like can be spontaneously curled to the desired degree of curvature by contacting the hair with a liquid bath containinga concentrated solution of sulfur dioxide and being at a temperature not substantially below 80 C. To give a specific example, the process. of this invention can be carried out by treating the hair with a saturated aqueous solution of sulfur dioxide (sulfurous acid) at a'tempenature of 95 C. for a period of about 8 to 15 minutes. Subsequent to this treating step additional steps can be employed, and these will hereinafter be described in detail.

It is believed that spontaneous curling of hair is dependent upon difierential shrinkage in various parts of the hair. The treatment produces not only a difierential shrinkage but an overall shrinkage in the length of the hair as well. It is desirable to minimize the overall shrinkage as much as. possible while maximizing the differential shrinkage. three distinct zones difiering from one another in cell structure but not difiering essentially in chemical composition. The outermost zone is known as the cuticle. The region immediately beneath the cuticle and usually comprising the major portion of the hair is known as the cortex; The center core of pulp-like nature which sometimes is present is known as the medulla. The differential shrinkage which we believe is the proper explanation for the spontaneous curling of the hair resulting from our treatment may be due to unequal rates of reaction between the sulfurous acid solution and these various layers. In any case curling necessarily implies differential dimensional changes between opposing sides of the hair in the plane of curvature. the treatment with sulfurous acid solution at tempera:

in some manner The cross-section of the hair indicates tures over 80 C. accomplish this ditferential dimensional change.

Because of the shortness of hog hair, and particularly hog hair collected during the summer season, it is important to keep the over-all shrinkage of the hair at a minimum. Therefore, it is an important advantage of employing sulfurous acid (sulfur dioxide in water) in treating hog hair to cause it to curl spontaneously that any desired degree of curl, or at least all commercially desirable degrees of curl, can be produced while limiting the longitudinal shrinkage to less than 10%.

Treatment with a reducing agent is not alone suificient to cause hair to curl spontaneously. It has been definitely determined during the development ofthis invention that nocurling of, consequence occurs at temperatures substantially below 80 C. regardless of the duration of the treatment and concentration of the reducing agent. In other words, in addition to being contacted with a solution of sulfur dioxide, the hair must also be exposed to temperatures in a liquid bath of 80 C. or above for a substantial period of time to bring about the spontaneous curling of the hair. Preferably, the treating bath is maintained at a temperature above about 90 C. When carrying out the treatment in an open system at atmospheric pressure, it has been determined that the optimum temperature is around 95 C., and that as the temperature is raised above 95 C. it isrnuch more difficult to obtain the desired degree of curl in the hair and that in the neighborhood of 100 C. the amount of curling which can be brought about is relatively slight. Therefore, when operating at a pressure of one atmosphere, the temperature range between about 90 and 97 C. is preferred.

The reason why better results are obtained at 95 C. than at 100 C. is probably related to the concentration of the sulfur dioxide solution, which has been found to be quite critical. To bring about any appreciable spontaneous curling of the hair, at least about 0.15% by weight of sulfur dioxide to the water must be present in the treating bath. The concentration of a saturated aqueous sulfur dioxide solution decreases sharply at temperatures above C., and at temperatures above about 97 C. at atmospheric pressure sutficient sulfur dioxide cannot be retained in the water to produce the desired result. However, temperatures in excess of 97 C. can be successfully employed by raising the pressure above one atmosphere. For example, at an absolute pressure of two atmospheres, a temperature of C. can be used.

Since the concentration of the sulfurous acid solution is a critical factor in effecting a curl in hair, it follows that the conditions of the system must be such that the solution retains at least the minimum 502 requirement for curling. These conditions include as variables both pressure and temperature. If the chosen pressure is atmospheric pressure the critical concentration of 0.15% can only be obtained at temperatures below 97 C. However, if super-atmospheric pressures are employed, it is possible to go to higher temperatures successfully. We believe that the higher temperature of treatment, up to say 110 C., the better are the resulting physical properties of the curled hair. The higher temperatures require shorter time of treatment and it may be that less polypeptide rupture occurs under these conditions. This might account for the somewhat better physical properties that we obtain at the higher temperature of treatment. For simplicity of operation, it may be preferable to carry out the treatment at atmospheric pressure.

At temperatures above 80 C., concentrations of about 1.5% by weight of sulfur dioxide in water are about as great as can be conveniently obtained, and therefore it can be said that at atmospheric pressure and temperatures above 80 C. the working range of concentrations is between about 0.15 to 1.5% by Weight of sulfur dioxide inv water. It is preferred in carrying out the treating step to continually add. enough sulfur dioxide to the aqueous solution to maintain. a saturated solution throughout the treatment. satisfactory results, since satisfactory spontaneous curling can be achieved by having the concentration of the solution within the specified range during a substantial portion of the treating period.

In general, it is preferred to carry out the treatment in a strongly acid pH range. However, operation in the correct pH range is automatically obtained by employing the correct concentrations. It has been determined that the minimum operable concentration of S02 in water, namely 0.15%, produces a pH of about 2 to 3, and that the more concentrated solutions produce pHs below 3 down to about pH 1. Prior work in this field suggested that the contacting of hair with reducing agents under strongly acid conditions would have a tendency to cause the polypeptide chain to be broken. Therefore, it would be expected that the use of sulfur dioxide in concentrations suificient to produce a pH of 3 or below would cause the physical properties of the hair treated under these conditions to be impaired. It was surprising to find that the desired physical properties of the hair such as tensile strength, stiffness modulus, and elongation at break, were substantially unimpaired by the treatment. Therefore, it would seem logical to assume that the polypeptide chains were not disrupted to any appreciable extent. In treating some types of hair, particularly cattle hair, some impairment of the. desired physical properties has been noted, although it is much less than would have been expected. In treating hog hair, however, there is substantially noimpairment of properties, and therefore the process of this invention is particularly well suited to spontaneously curling hog hair.

In carrying out the proces of thi invention, it is desirable to prepare a liquid bath having the required amount of sulfur dioxide dissolved therein, and it is preferred that the solvent employed in the liquid bath be water, although. other solvents can be employed, such as.

However, this is not essential to obtain mixtures of the lower alcohols and water, with a fair measure of success. The hair can then be contacted with the prepared solution in any suitable manner. Generally, it is preferred to immerse the hair in the solution until the desired degree of curvature is obtained. The time of contact of the hair with the solution can be varied from about 3 to 30 minutes. However, it is generally necessary to immerse the hair in the solution for at least 8 minutes. In actual practice, it has been found that very satisfactory control of the degree of curvature produced can be obtained by varying the contact time from 8 to 15 minutes. It has been found that the curl imparted to the hair can be controlled at will by varying the conditions of treatment; namely, concentration of sulfur dioxide, and time and temperature of treatment. It would have been expected that the prior history of the hair, which includes both the conditions under which the hair is removed from the animal and the subsequent treating procedures for cleaning and sterilizing the hair, would be an important factor in causing the hair to curl a particular amount. However, it has been found that when employing sulfur dioxide as a reducing agent that the prior history of the hair does not appear to appreciably afiect the degree of curl obtained under comparable treating conditions. Chemical curling produces a sort of haphazard, 3dimensional curvature in the hair filament, which not only varie from point to point as to radius, but also varies in direction. Therefore, the exact measurement of the degree of curl presents a diflicult problem. However, it can be stated in general that the desired physical property of the hair is the development of random shapes in the hair filament which will enable them to be positioned in bulk so as to produce the lowest possible apparent specific gravity. As compared with chemically curled hair, mechanically curled hair probably has more hairs curled in a constant direction and possibly at a more constant curvature. However, the mechanically curled hair may have a substantial portion of the hairs which have escaped proper curling, and the controllability of the statistical curl is not nearly as precise as that which can be obtained by chemical curling.

There is another factor which is of importance in determining the amount of curvature which will be produced in the treated hair. This factor is the diameter of the hair itself. Controlled curling of hair can be most easily produced in hair of a type having an average diameter between about 2.5 to 9.0 rmls. However, filaments such as wool having an average diameter of about 1 mil or less can be satisfactorily curled, although this process has been found particularly successful with the coarser types of hair.

After the completion of the step of treating the hair with sulfur dioxide, it is preferable to wash the hair to free it of residual chemicals. Water or other suitable solvents can be used for this washing operation. If desired, however, the washing step can be omitted without serious effect. Following the washing step, or immedi ately after the initial treating step if the washing step is omitted, it has been found desirable to dry the hair under conditions and in a manner which will enhance the curl of the hair. The drying of the hair can be carried out in a variety of ways, but it is preferred to dry the hair by directing a stream of warm air (above 75 C.) through the mass of hair, and simultaneously agitating the hair. Preferably, the air is heated to about 100 to 115 C. The agitation of the hair can be accomplished in any suitable manner such as by tumbling in a rotary drier, by raking on a fiat belt conveyor, or by any other convenient method. It has been found that the combination of drying and agitation improves the curl and loft of the hair.

The result of the sequence of steps described above is that hair having any desired amount of curl can be obtained without impairing the desirable physical properties of the hair as shown by measurements of the tensile strength, elongation at break, and stiffness modulus of the hair before and after curling. Hog hair has been found to respond particularly well to the curling process of this invention, since the impairment of desirable physical properties is so slight that there is little reason for attempting to improve the physical properties of the hair after treatment. However, in curling other types of hair by the method of this invention, there is some slight impairment of desirable physical properties, and therefore prior to the drying step the hair can be treated to improve its physical properties. j

As indicated above, it has been believed for sometime that the disulfide cross-linkages between the polypeptide chains can be restored after being broken by a reducing agent by treating the hair with either a cross-linking agent which is capable of inserting an alkyl group between two sulfur atoms in different polypeptide chains, or by treating the hair with an oxidizing agent capable of causing the disrupted sulfur to sulfur cross-linkages to reform. It is believed that the reconstruction of the disulfide crosslinkages by either of these methods somewhat improves the physical properties of the hair, such as tensile strength and resiliency. It has been found that when sulfur dioxide is used as a reducing agent it is preferable to treat the hair with an aqueous solution of formaldehyde which is believed to react between the sulfhydryl groups to effect the substitution of an alkyl di-thio-ether linkage for the disulphide linkage. Quite possibly it may also react with amino groups to effect additional cross-linkages. Other lower alkyl aldehydes, preferably containing less than 5 carbon atoms, such as glyoxal can be used instead of formaldehyde with satisfactory results. Also, alkyl di halides such as ethylene dibromide can be employed. While the introduction of an additional group between the sulfur atoms is preferred, the reconstruction of the surfur bonds by the use of an oxidizing agent is also of value. A wide variety of common oxidizing agents yielding oxygen readily can be employed such as potassium or sodium bichromate, potassium permanganate, potassium chlorate, and hydrogen peroxide. In the treating of the hair with either a cross-linking agent or an oxidizing agent, it is in general preferred to prepare an aqueous solution of the chemical and to immerse the hair in the solution for a sufficient time to bring about the desired action. This step, however, can be carried out in accordance with procedures well-known in the art, and therefore it is believed that it will not be necessary to further describe it herein.

The following examples are set out in order to more fully illustrate the method of this invention:

Example I 1250 gms. of cattle tail hair was placed in a stainless steel pail containing 7500 gms. water heated to 93 C. Sulfur dioxide Was bubbled into the bottom of the pail through a sparger and the flow maintained at a rate that would insure a saturated solution throughout the duration of the treatment. At the end of 15 minutes the hair had assumed a curled form and it was then removed from the pail, and placed in an 0.5% solution of formaldehyde at C. for 15 minutes. The hair was then removed from the solution and dried in a stream of air heated to about C. while being continuously tumbled.

The physical properties, as determined at 65% R. H. (relative humidity) and 70 F., were as follows:

.7 Example -II 125.0 g'ms. "of winter hog 'hai'r was placed in a-stainless sfee'l pail containing 7 5 gm. water. "Sulfur dioxitie' was introduced into the solution while maintaining the "temperature'at 93 Cxland the flow maintainedataratethat would insurea'saturateds'dlution throughout" the duration df'the-treatment. When-the hair had 'assunredthe degree of "curl desired it was removed from "the solution, rinsed briefly with water, and dried in a str am-of air "heated to 100 -C. while being continuously tumbled.

The resulting hair had the desired curl and :in bulk possessed th'edes'i're'd loft and low density. The physical properties, asdterhiihed at 65% R. H. and70 F. were asiollows:

: Original Curled Hail" Hair hsi/s'qiinn .percent... -3 lbs/sq. in '700, 000

:For comparison, the tensile -.strength on cufledzhog hair; prepared -by the usual method of rope spinning-and setting with boiling water averages about -3 6,-000.-lbs, per sq. Elongation at break is about 22% and tensile modulus 650,000 lbs. per sq.-in.

Example III 1250 gms. of cattle tail hair was placed in a-sta-i'nless steelrpressure vessel containing 7500 gms. of water preheated'to 95 C. I he vessel' was sea'led, the temperature raised to .105 =C., and sulfur dioxide then introduced through a 'sparger in the bottom of the pressure vessel:-

orig-mar 'Curled Hair Hair Tensile Strength;- -;lbs./sq.'in Elongation at Break oercent Tensile Modulus lbs./sq. in

Example IV 1250 'gms. o'fh'orse tail hair was placed in a stainless steel "pail containing 7500 lgm. water. Sulfur dioxide was bubbled into the Water while maintaining the temperature at 93 (3., and the iflow maintained at a rate that would insure a saturated solution throughout the duration of the treatment. At the end of 12 minutes the hair'was removed :from the sulfurous acid solution, rinsed with water, and placed in an '0.'5%' solution of sodium bichroniate at 25 C. for '15 minutes. The hair was'then removed, again rinsed in'water, and dried in a stream of heated air.

Curled Hair Original Hair Tensilehtrength lbs./sq. in. Elongation at .Break .percent. TensileModulus 1bs./sq. in-

It will be apparent from the foregoing that the method Of this invention can be readily adapted to carrying 8 outacontinuousprocess. I orexample, can be done byemploying one or more tanks through which conveyor-s travel, each :tank containing the appropriate solution of a chemical treating agent at the .proper temperature, and the hairprogressingat acontrolled.rate through eachtank.

-An important application 'of curled hair, and 'in particular-curled -:hog hair, is in cushions prepared by treating an arranged =mass of curled :hair with latex or the equivalent, then drying-and curing'the structure to secure a resilient pad of light density in which the hairs are sheathed with rubber and bonded together at tpointsof intersection.

. :Ha'ir curled -by the method herein describedisadmirably suited for making into rubberized hair cushions. The control "of density "of'thesecushions is important in determining the load compression characteristics. The compression modulus in a rubberized hair cushion is determinediin large measure by the density of thepad and an important factor-in-this is the degree :ofcurvature and'the length of-thehair used. Since the method herein described for=curling hair can .produce any desired degree of =curl simply -by altering the time 'of treatment, and can be einployedon any hair regardless of'length, it is ideal for preparing hair for rubberized hair-cushions;

While in the foregoing specification :this 'inventionhas been described in detail for purpose (if-illustrating various embodimentsthereof, it will be'readily apparent to those skilled in the :art that many 0f the details specified can be 'varied widely without'departing from the spirit oftheinvention.

We claim:

1. The method 'of spontaneously curling animal "hair, comprising treating detached non-human animalhair filaments by impregnating said filaments with 'Water c'ontaining :at least =05l5% by weight sulphur dioxide while being atapH less than about pH 3, and at a temperature ranging from C. up to the highest temperatureat which said*0.-l5% sulphur dioxide concentration ca'n be maintained, and continuing said impregnating treatment until the desired degree-of curl is obtained.

-2. The-methodof claim l in which said detached animal hair filaments are selected from the group consisting of hog hair, cattle hair and horse hair filaments.

3. The method of claim 1 in which said detached animal hair filaments are'hog hair filaments.

4. The method of spontaneously curling animal hair, comprising immersing detached non-human animal hair filaments under=atmosphericpressure in an aqueous bath containing at least 0.15% by Weight sulphur dioxide -'at a temperature ranging from to 97 C. until the desired degree 'of curl is obtained, said aqueous bath 'being at a-pH-of below 3.

5. The method of claim 4 in which said detached animal hairfilaments are hog hairiilaments.

6. The methodof spontaneously curling detached animal hair filaments selected from the-group consisting of hog hair, cattle hair and horse hair, comprising immersing said'detached animal hair filaments in 'an aqueous 'bath containing from-0.15 to 1.5% 'by weight sulphur dioxide at a temperature ranging-from 80 C. up to the-highest temperature at which the sulphur dioxide concentration thereof can bemain'tained withinsaid 0.1510 1.5% range, and maintaining said filaments in contact with said bath until the desired degree of curl is obtained, said bath being at apI-Inot substantially over 3.

7. The method of spontaneously curling animal hair, comprising treating detached non-humananimal hair'filaments by impregnating said-filaments with water containing at 'least 0;15 by-Weight sulphurdioxide while being at a pH below 3 and at a temperature ranging from 80' C. up to the 'highest temperature at which said 0. 15% sulphur dioxide concentration can be maintained, contuning said impregnating treatment 'until said filaments are :given :a pronounced de'gree of curl, and then drying 9 the curled filaments while simultaneously agitating them to enhance the curvature thereof.

8. The method of claim 7 in which said detached animal hair filaments are hog hair filaments.

References Cited in the file of this patent UNITED STATES PATENTS Elsasser Nov. 7, 1911 10 Speakman June 20, 1944 Speakman Oct. 29, 1946 OTHER REFERENCES Journal of the Textile Institute, July 1941, pp. T95 and T102.

Journal of the Society of Dyers and Colorists, September 1936, p. 338. 

1. THE METHOD OF SPONTANEOUSLY CURLING ANIMALS HAIR, COMPRISING TREATING DETACHED NON-HUMAN ANIMALS HAIR FILAMENTS BY IMPERGNATING SAID FILAMENTS WITH WATER CONTAINING AT LEAST 0.15% BY WEIGHT SULPHUR DIOXIDE WHILE BEING AT A PH LESS THAN PH3, AND AT A TEMPERATURE RANGING FROM 80* C. UP TO THE HIGHEST TEMPERATURE AT WHICH SAID 0.15% SULPHUR DIOXIDE CONCENTRATION CAN BE MAINTAINED, AND CONTINUING SAID IMPREGNATING TREATMENT UNTIL THE DESIRED DEGREE OF CURL IS OBTAINED. 